Abstract: A method and apparatus for treatment of the fly ash are described wherein heavy metals are separated and wherein there is formed a leaching resistant slag; the fly ash is introduced into a reactor into an oxidizing gas stream which is heated to at least 2500 degrees C. in a plasma generator; the fly ash melts and forms liquid drops of slag and a carbonaceous or hydrocarbonaceous material is added to the gas stream which burns and supplies extra energy to the process; the ratio of oxygen and carbon is regulated so that the ratio CO.sub.2 /CO+CO.sub.2 is kept within the limits 0.4-0.